1. Field of the Invention
The present invention relates to the measurement of a gap between nipped components through which a paper web is being passed, and, more particularly, this invention relates to a system for measuring the nip gap in a paper-making press apparatus through which a traveling flexible material is passed for dewatering the paper web.
2. Description of the Related Art
In the press section of a paper-making machine, water is typically removed mechanically by passing the paper web through a nip between structural components, such as two rotating rolls. The nascent paper web is carried on a felt for absorbing the water expressed from the paper web as it passes through the nip.
One of the characteristics of a quality paper product is uniformity of caliper in a cross-machine direction of the paper-making machine. Such uniformity of caliper is difficult to obtain, particularly in bulky products, such as tissue and towel grades, due to deflection of machine components caused by gravity.
Rolls of different design, such as control-deflection rolls and plain rolls, deflect different amounts along their lengths extending in a cross-machine direction. A non-uniform gap, or uneven gap loading in the cross-machine direction, will produce undesirable variations in both caliper and moisture in the web passing through on its way to the dryer section. Such variations undesirably affect the processing of the web, such as by requiring costly special profiling downstream of the press section, increasing expensive thermal removal moisture in the dryer section, or slowing the entire paper-making machine.
What is needed in the art is a way of measuring the gap between the surface which presses the belt against the support surface and signals that measurement so that the gap can be changed or adjusted according to predetermined design parameters.